This invention relates to a process for producing a top bar for carding machines, which comprise a hollow profile formed by cold drawing and shaping a sheet of metal. The bar has a clothing receiving surface and a back part raised in the form of a T-cross section relative to the clothing receiving surface.
In the past, top bars have been produced from cast iron and have a T-shaped cross section for reinforcement or stiffening. Such bars are heavy and sag under their own weight, especially on very wide carding machine. This sagging causes an impairment of the carding action. Furthermore, the flat drive on revolving flat cards is subjected to undue loads as a result of the heavy weight of the cast iron top bars.
There have also been attempts to produce top bars from hollow profiles such as those shown in German patent specification no. 384,195 and in German Patent No. 409,319. In each of these references, hollow profiles of a T-shaped cross section or of a triangular cross section are produced by bending a sheet of steel into the finished position or final shape and closing the seam of the profile by welding. This procedure is very expensive and also has the disadvantage that the bending results in a less than uniform dimensions with thermo-stresses therein as a result of the later welding operation. Latent stresses and the like imparted to the sheet by the bending step may also cause the bar to be less rigid or to even change its configuration during usage. This problem is accentuated when long top bars are produced for the very wide cards in usage today.
The width of the new cards require very precise dimensions wherein a rigid top bar measuring over one meter in length has the necessary rigidity to provide the necessary surface for supporting the card clothing thereon. It is very important that the top bar be very rigid and present an even surface throughout its length for the support of the card clothing. The reason for this is that the clothing on the top bar must cooperate with the clothing on a card cylinder during the carding operation. The clothing on the card cylinder is ground to a perfectly uniform height throughout its length and the clothing on the top bar must also present a uniform surface throughout its length. If the top bar is permitted to sag due to the weight of the bar or a lack of sufficient rigidity therein, the carding process will be defective at the points that the top bar sags and insufficient carding of the fibers will be obtained.